HIV vaccine: first step to a cure or a false dawn?

Following the limited success of HIV vaccine trials in Thailand, there are hopes that scientists may have made a significant breakthrough in the fight against the disease.

The trial, which used a combination of two previously unsuccessful vaccines, was carried out on 16,000 Thai men and women between the ages of 18 and 30. After half were given the vaccine and half a placebo, the number of people who had taken the vaccine and then acquired the disease was almost a third (31 per cent) lower than the rate of infection in those who had taken the placebo.

The $105m study was organised by the US Army and the Thai Ministry of Public Health. Colonel Jerome Kim, the US Army's HIV vaccines product manager, called it "the first evidence that we could have a safe and effective preventive vaccine".

After the desperately disappointing failures of the two previous vaccine tests of this scale in 2003 and 2007, the response of the scientific community has been one of cautious optimism. There still remains a lot to examine - whether this vaccine will be as effective against different HIV subtypes, the need for additional boosters, and whether it will work in high-risk groups such as intravenous drug users.

Commentators have been discussing the true significance of this apparent breakthrough.

WHAT THEY'RE SAYING:

Elizabeth Pisani, the Times: If I know I have been vaccinated, will that make me more likely to share needles, or less likely to use condoms? And if it does, will that change outweigh the 30 per cent reduction in risk that comes with the vaccine? The question came up in 2005, when studies showed that circumcising men reduced their risk of getting HIV through heterosexual sex by 60 per cent. A stunning result, but one that health authorities didn't act on for years because they worried that circumcised men would enjoy what the wonks call "behavioural disinhibition" - that "I've been snipped, so I can toss the condoms" thinking.

Andy Coghlan, New Scientist: One slightly worrying finding is that people who did become infected had similar levels of virus in their blood whether or not they'd been vaccinated. This suggests that if vaccinated people do get infected, their immune systems still struggle to combat the virus.

Dr Peter Klatsky, Huffington Post: While the media loves a big story, these results were underwhelming. Although they were "statistically significant", it is way too early to declare success. A simple look at the numbers is more sobering: after vaccinating 16,000 people, there were 23 fewer new infections in patients receiving the vaccine (51 cases versus 74 cases). If one additional patient who received the vaccine became infected (52 instead of 51) the results would no longer be "statistically significant."

Leader, the Independent: After the failure of the four trials, pessimism within the scientific community grew and some scientists predicted a vaccine would never be found. Meanwhile, dissenting voices within the Aids community demanded the resources devoted to vaccine research be diverted into safer sex, condom distribution and other preventive measures. Drugs to treat HIV have been successful in converting a disease that was once a death sentence into a chronic condition. But no one has ever been cured of HIV. Preventing the infection remains the best strategy. ·